Increasingly high demands are made on internal combustion engines with regard to their performance and efficiency. At the same time, because of stringent legal regulations, the emissions must also be low. Such requirements can be met properly if the internal combustion engine is equipped with gas-changing valves and corresponding drives for this internal combustion engine in which the valve lift curve differs depending on the operating point of the internal combustion engine. Because of this, throttle losses in the case of air intake can be reduced and, if required, higher exhaust gas recirculation rates can quickly be set.
Adjusting the valve lift of a gas intake valve of the internal combustion engine between a lower and a higher valve lift is known. The Porsche 911 Turbo for example is thus equipped with a device for adjusting the valve lift of the gas intake valve and the gas outlet valve. In addition, the internal combustion engine of this vehicle is provided with a camshaft on which for each gas intake valve, one cam with a lower lift and two additional cams with a higher lift are embodied. The cam lift is transferred by means of a transfer unit to the gas intake valve. The transfer unit is embodied as a cup-shaped tappet comprising a cylinder element and a ring cylinder element arranged concentrically to this cylinder element. The cam with a lower lift acts on the cylinder element while the cams with the higher lift act on the ring cylinder element. Depending on a switch position of the cup-shaped tappet, either the lower or the higher lift is transferred to the gas intake valve. While the internal combustion engine is idling, the lower cam lift is transferred to the gas intake valve. This results in lower frictional losses based on the small diameter of the cam and the cylinder element used in this mode of operation and the lower valve lift.
In addition, a higher loading movement is achieved. This enables the emissions of the internal combustion engine to be decreased and at the same time, the fuel consumption to be kept low. The lower valve lift is maintained in the case of a lower and average load. Throttle losses can also be reduced by a corresponding phase adjustment between the gas intake valve and the gas outlet valve and a resulting internal exhaust gas recirculation rate. In the case of higher load requirements made on the internal combustion engine, the valve lift passes to the higher value. For a high driving comfort of a vehicle in which such an internal combustion engine is arranged and for low emissions of noxious substances, it is important that the passage from the lower valve lift to the higher valve lift takes place without misfiring.